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Unix was not designed with security primarily in mind. It was initially developed in the late 1960s -- before the Internet was invented. While relatively simple, the Unix security model is inadequate for protecting against common security threats. Its designers identified fundamental design flaws over thirty years ago. As Linux is modeled on Unix, it inherits this traditional Unix security model. Meeting modern security requirements has required significant enhancements to Linux, which are ongoing, but well-advanced. While many new security ideas have emerged, Linux developers have necessarily been constrained by decades of operating system standards and conventions. Aimed at admins, developers and technical managers, the talk will cover:* The historical context of Linux security * Modern security OS requirements * How these requirements are being addressed (or not) by various enhancements made to Linux security * Areas of ongoing and future work. We'll also consider how FOSS culture contributes to security.
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Linux Kernel Security
Adapting 1960s Technology to Meet 21st Century Threats
James MorrisRed Hat
LinuxCon Boston 2010
History
Fig. 1
“The first fact to face is that UNIX was not developed with security, in any realistic
sense, in mind; this fact alone guarantees a vast number of holes.”
Dennis Ritchie, “On the Security of UNIX”, 1979
Unix DAC
Fig. 2
DAC is “simple” and somewhat effective, but inadequate for modern environment:
Does not protect against flawed or malicious code
(Actually, DAC is not simple)
Fig. 3
“It must be recognized that the mere notion of a super-user is a theoretical, and usually practical,
blemish on any protection scheme.”
(also from Ritchie 1979)
Enhanced DAC
Fig. 4
POSIX Capabilities (privileges)
Access Control Lists (ACLs)
Namespaces
Fig. 5
Network Access Control
Netfilter
iptables
ebtables
Fig. 6
CryptographyFig. 7
Disk Encryption:
dm-cryptecryptfs
Network Encryption:
IPsec
ASLR
NX
GCC
/dev/mem
Kernel pointers
System Hardening
Fig. 8
The Inevitability of Failure
The Flawed Assumption of Security in Modern Computing Environments
Fig. 9
Mandatory security
Trusted / protected path
Assurance
Linux Security Modules
READ LSM Hook
LSM Module
SELinux
Generalized MAC
Very fine-grained
Policy-flexible
Simplified Mandatory Access Control Kernel (SMACK)
Simple label-based MAC
Policy is written as triples:
subject object [–rwxa]
TOMOYO
Path-based MAC scheme
Automatic real-time policy generation
Policy applied to trees of process invocation
AppArmor
Pathname access control scheme
Security usability via familiar abstractions
Extending MAC
Netlabel
Secmark
NFSv4
sVirt
Audit
Required for certification
Monitor syscall, LSM & misc. security events
Actually quite useful
Integrity & Platform Security
TPM
IMA / EVM
TXT
VT-d
Anti Malware
Best done in userland
... but, file scanning still desired
fsnotify
fanotify
Seccomp
Extremely lightweight sandboxing
Reduces attack surface
Current Status
Meets extremely wide range of security goals
Security features now mainstream
Better equipped to address modern threats
Ongoing Challenges
Continued refinement & hardening
Multiple security models hindering adoption
Threats will continue to evolve
How to Help
Enable features
Report problems
Share knowledge
Fig. 10
Resources
Linux Kernel Security Wiki
LSM Mailing List
LWN Security page
Questions ?
Useful URLs
Kernel Security Wikihttp://security.wiki.kernel.org/
LSM Mailing Listhttp://vger.kernel.org/vger-lists.html#linux-security-module
LWN Security Pagehttp://lwn.net/Security/
“The Inevitability of Failure: The Flawed Assumption of Security in Modern Computing Environments”
http://csrc.nist.gov/nissc/1998/proceedings/paperF1.pdf
LSM Usenix Paperhttp://www.usenix.org/event/sec02/wright.html
Kernel Memory Protectionhttp://lwn.net/Articles/329787/
Linux Security Model Comparisonhttp://tomoyo.sourceforge.jp/wiki-e/?WhatIs#comparison
Useful URLs ...SELinux
http://selinuxproject.org/“Have You Driven an SELinux Lately?” (OLS paper on current state)
http://namei.org/ols-2008-selinux-paper.pdf“Anatomy of Fedora Kiosk Mode”
http://namei.org/presentations/fedora-kiosk-mode-foss-my-2008.pdf“SELinux Memory Protection Tests”
http://people.redhat.com/drepper/selinux-mem.html“A seatbelt for server software: SELinux blocks real-world exploits”
http://www.linuxworld.com/news/2008/022408-selinux.html
SMACKhttp://schaufler-ca.com/
AppArmorhttp://en.opensuse.org/Apparmor
TOMOYOhttp://tomoyo.sourceforge.jp/
“POSIX file capabilities: Parceling the power of root”http://www.ibm.com/developerworks/library/l-posixcap.html
“POSIX Access Control Lists on Linux”http://www.suse.de/~agruen/acl/linux-acls/online/
Useful URLs ..."Implementing Native NFSv4 ACLs in Linux"
http://lca2009.linux.org.au/slides/79.tar.gz
“Applying mount namespaces”http://www.ibm.com/developerworks/linux/library/l-mount-namespaces.html
“Disk encryption in Fedora: Past, present and future”http://is.gd/16012
“Limiting buffer overflows with ExecShield” (2005)http://www.redhat.com/magazine/009jul05/features/execshield/
“Linux Kernel Heap Tampering Detection”http://phrack.org/issues.html?issue=66&id=15#article
“System integrity in Linux”http://lwn.net/Articles/309441/
“Linux kernel integrity measurement using contextual inspection” (LKIM)http://portal.acm.org/citation.cfm?id=1314354.1314362
Intel TXT Sitehttp://www.intel.com/technology/security/
IBM TCPA Resources http://www.research.ibm.com/gsal/tcpa/tcpa_rebuttal.pdf
Invisible Things Labs http://theinvisiblethings.blogspot.com/
Image Credits
1. Bell Labs
2. Duke University Ad*Access
3. Hao Chen, David Wagner, and Drew Dean.
4. “nofeel” (flickr)
5. Unknown
6. Ian Lloyd (flickr)
7. James Morris
8. Steve Jurvetson (flickr)
9. Michael Scott (flickr)
10. Alfred T Palmer (LoC)
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